The invention relates to an internal combustion engine of rotary valve design, in which the sealing of compressed gases is achieved automatically. The state of the art as discernible from technical literature demonstrates that the limitations on internal combustion engines, in terms of noise levels and running speed, are dictated at least in part by the embodiment of the inlet and exhaust valves by which operation of the engine is adjusted and controlled; such an observation applies to Otto and Diesel units alike.
Current literature similarly shows that the means of overcoming such limitations lie in the adoption of rotary valves to replace the conventional poppet type.
More exactly, the traditional poppet valve is a reciprocating component, returned by spring means; thus, the number of cycles it is able to accomplish necessarily depends on the properties of the spring means, and its service life is ultimately limited. Moreover, the reciprocating movement of the poppet valve is such as to produce a metal-on-metal impact at the end of each stroke, hence a certain level of noise.
By contrast, the movement of a rotary valve permits of obtaining particularly high running speeds and singularly low noise levels, since no spring return means are employed, and there is no stroke impact. Furthermore, rotary valves are capable of offering greater cross sectional areas to the flow of gases, thereby increasing efficiency of the engine; again, with the rotary valve design, combustion chambers can be made more compact and positioned directly in the flow path of inlet and exhaust gases.
On the debit side, rotary type valves are beset by a problem as yet unresolved, namely, that of their unsatisfactory sealing action, which is so poor in practice as render them unsuitable for the mass production of internal combustion engines. Faultless sealing action is in fact indispensable to correct operation of the engine, inasmuch a loss of pressure from the combustion chamber results in loss of output, hence in substandard operation of the engine as a whole.
Securing an efficient sealing action, difficult enough in rotating parts generally, becomes still more problematical in the case of the i.c. engine, given that pressure and temperature are cyclic rather than constant, and reach particularly high values.
The difficulty in question is also attested by the considerable number of patent specifications that have been published on the subject, most of which disclosing sophisticated and complicated sealing arrangements which not only fail to offer a full solution to the problem, but are quite unacceptable from the cost standpoint.
For example, application DE-OS No. 3241722 for German patent sets forth the expedient of hardening one of the valve's two mating surfaces and dry-lubricating the other, which is less hard. Hardening is brought about by a variety of techniques from quenching of the bare metal to application of a ceramic facing, or again, using a separate bushing fitted with the assistance of force or heat; the dry lubrication is achieved with carbon or molybdenum sulphide. Clearly enough, such a remedy is so costly and difficult to implement as to be suitable only for special applications where the time and expense can be justified; similarly, purpose-designed, costly equipment is required in servicing such seals. U.S. Pat. No. 4,517,938 discloses a rotary valve device in which use is made of numerous rings, and of dry seals associated with the valve bearings. Here too, the parts in mating contact are variously embodied in materials including sintered, carbon, and those with a low coefficient of thermal expansion or low conduction of heat.
Whether in the case of the references cited above, or of others not mentioned though directed toward this same question of improving the sealing action of rotary valves, none of the expedients proposed succeed in providing a technically complete and rationally comprehensive solution to the problem; at all events, the resulting prior art consists in methods based on the use of an extensive number of interconnected components, the failure of just one of which can adversely affect smooth operation of the engine as a whole, and besides, there is the basic cost of the single components, which clearly adds to the cost of the assembled engine.
Accordingly, the object of the present invention is to provide a definitive solution to the problem of poor sealing action in rotary valves for internal combustion engines, with such a degree of economy as will justify its adoption on industrial scale, not only from the manufacturing standpoint, but also from that of subsequent servicing; in effect, the necessary operations can be performed by semi-skilled persons and without any need for special equipment.
It is an additional object of the invention to design an internal combustion engine with rotary inlet and exhaust valves the construction of which is such as to permit a significant reduction in the cost of manufacture, thanks to a reduction in the number of parts, and ensure lower noise levels with the engine running.